Coating materials of this kind are known from, for example, WO 08/74491, WO 08/74490, WO 08/74489, WO 09/077181 and WO 10/149236. The compound (B) used in these coating materials, containing isocyanate groups and silane groups, is based on known isocyanates, preferably on the biuret dimers and isocyanurate trimers of diisocyanates, more particularly of hexamethylene diisocyanate. These coating material compositions have the advantage over conventional polyurethane coating materials of a significantly improved scratch resistance in combination with good weathering resistance. In need of improvement with these coating materials, however, are the sandability and polishability of the resultant coatings.
Furthermore, EP-A-1 273 640 describes two-component coating materials comprising a polyol component and a crosslinker component, consisting of aliphatic and/or cycloaliphatic polyisocyanates or the polyisocyanates derived therefrom by polymerization, allophanate formation, biuret formation or urethane formation, where 0.1 to 95 mol % of the originally free isocyanate groups present have undergone reaction with bisalkoxy-silylamine. These coating materials can be used for producing clearcoats or topcoats in the automotive sector, and, following their complete curing, exhibit good scratch resistance in combination with good resistance to environment effects. This specification, however, contains no information on how the sandability and polishability of the resulting coatings can be improved.
WO 07/033786, furthermore, discloses coating materials which as well as phosphonic diesters and diphosphonic diesters, as catalyst (A), comprise silane-group-containing mixtures (B), such as, for example, the mixture of the isocyanate-group-free reaction product (B1) of hexamethylene diisocyanate isocyanurate with N,N-bis(3-trimethoxysilylpropan-1-yl)amine and the isocyanate-group-free reaction product (B2) of isophorone diisocyanate isocyanurate with N-(3-trimethoxysilylpropan-1-yl)-N-n-butylamine, and also optionally, as further additives (C), polyacrylate resins or other binders and crosslinking agents. According to their hardness, the coatings produced from these coating materials again exhibit good scratch resistance combined with good resistance towards chemicals and environmental effects, but the weathering resistance is in need of improvement and the resultant coatings are decidedly brittle. Additionally, here again, there is a lack of details as to how the sandability and polishability of the resultant coatings can be improved.
WO 2001/98393 describes two-component coating materials comprising a polyol as binder component and also, as crosslinker component, a mixture of a polyisocyanate (A) and a silane oligomer (B) which contains at least two isocyanate groups and additionally alkoxysilane groups, preferably bisalkoxysilane groups, and which is prepared by reaction of a polyisocyanate (PI) with alkoxysilylamines, preferably with bisalkoxysilylamines, more particularly with bis(3-propyltrimethoxy-silyl)amine. As polyisocyanate (A) and also as polyisocyanate (PI) for preparing component (B) it is preferred to use hexamethylene diisocyanate and isophorone diisocyanate and also their biurets and isocyanurates. These coating materials are used more particularly as primers and are optimized for adhesion to metallic substrates, preferably to aluminum substrates. Details of how the scratch resistance, on the one hand, but also, at the same time, the sandability and polishability of the resultant coatings may be improved are, however, not present in this specification.
It is known, moreover, from US 2006-0217472 A1 that the scratch resistance of coatings based on polyurethanes may be improved by taking coating materials which comprise a hydroxyl-group-containing binder, an isocyanate-group-containing crosslinker and a metal catalyst for the OH/NCO reaction and adding thereto an amino silane, such as bis(3-propyltrimethoxysilyl)amine, for example, or reaction products thereof with isocyanates.
WO 07/037857, lastly, discloses coating materials which as well as polyhydroxyl-group-containing compounds and polyisocyanate-group-containing compounds comprise 1% to 10% by weight of a silylated dimer fatty acid alcohol obtained by reaction of dimer fatty acid alcohol with isocyanate-functional silanes. The coatings obtained using these coating materials are notable in particular for a very high gloss. As the fraction of the silylated dimer fatty acid alcohols in the coating materials goes up, the hardness and the resistance towards solvents, measured in terms of double rubs with methyl ethyl ketone, of the resultant coatings goes down. In the automotive finishing sector, however, the requirement is increasingly for coatings featuring improved hardness and durability and hence an improved scratch resistance.
A problem addressed by the present invention, therefore, was that of providing coating material compositions, more particularly for automotive OEM finishing and automotive refinishing, that lead to coatings that are scratch-resistant to a high degree and more particularly exhibit high gloss retention after scratch exposure. At the same time, however, the resultant coatings ought also to ensure good sandability and good polishability.
Furthermore, coating material compositions ought to be provided that lead to a network that is weathering-stable to a high degree and that, at the same time, ensure high acid resistance. Moreover, the coatings and paint systems, especially the clearcoats, ought to be able to be produced even in film thicknesses >40 μm without stress cracks occurring. The coating materials, furthermore, ought to meet the requirements typically imposed on the clearcoat of automotive OEM finishes and automotive refinishes.
The new coating materials, lastly, ought to be preparable easily and very reproducibly, and ought not to present any environmental problems in the course of paint application.